Electromagnetic clutch

Abstract

Disclosed is an electromagnetic clutch comprising a field member with an exciting coil member disposed therein; a shaft extending through the field member and the exciting coil member; a rotor member fixedly disposed on the shaft at a position opposing to the filed member; a drive mechanism rotatably provided on the shaft; a contact member provided on the drive mechanism on the side facing the rotor member; an elastic member disposed on the drive mechanism for biasing the contact member to the drive mechanism. The contact member is positioned to form a clearance of a first dimension G1 along the shaft between the surfaces of the contact member and the rotor member and the first dimension G1 is set to be smaller than a limit dimension G3. A deformation of the elastic member by the limit dimension along the axial direction results in the elastic limit. The electromagnetic clutch has a restricting member provided on the drive mechanism for restricting a displacement of the contact member along the axial direction of the shaft to be less than a second dimension G2. The dimension G2 is set within a range between the first dimension G1 and the limit dimension G3.

What is claimed is: 
     
       1. An electromagnetic clutch comprising: a field member with an exciting coil member disposed therein;   a shaft extending through the field member and the exciting coil member;   a rotor member fixedly disposed on the shaft at a position opposed to the field member;   a drive mechanism rotatably received on the shaft;   a contact member provided on the drive mechanism on a side thereof facing the rotor member;   an elastic member fixedly connected to the contact member and disposed on the drive mechanism for biasing the contact member to the drive mechanism;   the contact member being positioned to form a clearance of a first dimension along the shaft between opposed surfaces of the contact member and the rotor member, the first dimension being set smaller than a limit dimension representing a distance of travel of the contact member away from the drive mechanism along an axial direction of the shaft translating into a maximum deformable amount of the elastic member, a deformation of the elastic member by movement of the contact member away from the drive mechanism an amount corresponding to the limit dimension resulting in reaching an elastic limit of the elastic member; and   a restricting member provided on the drive mechanism for restricting a displacement of the contact member along the axial direction of the shaft a distance less than a second dimension, the second dimension being set within a range between the first dimension and the limit dimension, movement of the contact member away from the drive mechanism being restricted to the distance less than the second dimension prior to reception of the drive mechanism on the shaft, thereby preventing deformation of the elastic member beyond the elastic limit thereof by an external force applied thereto.   
     
     
       2. An electromagnetic clutch according to claim 1, wherein: the drive mechanism includes a bearing housing into which a bearing is fitted to support the drive mechanism on the shaft;   the contact member is disposed outwardly around the bearing housing; and   the restricting member includes a tubular portion to be fitted onto an outer surface of the bearing housing, a first flange member at one end of the tubular member to be engageable with a side surface of the contact member, and a second flange member at the other end of the tubular member for attaching the restricting member to the drive mechanism.   
     
     
       3. An electromagnetic clutch according to claim 2, wherein a recess is formed on the rotor member on a side facing the contact member for enclosing the first flange member of the restricting member therein. 
     
     
       4. An electromagnetic clutch according to claim 1, wherein: the elastic member is a hollow disk shaped spring; and   the contact member is disk shaped and is fixed to the elastic member at a first radial distance thereof.   
     
     
       5. An electromagnetic clutch according to claim 4, wherein: the elastic member includes an arc shaped hole formed at a second radial distance thereof, the first radial distance being greater than the second radial distance.   
     
     
       6. An electromagnetic clutch according to claim 4, wherein: the restricting member is cylindrically shaped and includes a first flange at an end thereof facing the rotor, and a second flange at a remaining end thereof facing the drive mechanism.   
     
     
       7. An electromagnetic clutch according to claim 6, wherein: the second flange is fixed to the drive mechanism with the elastic member disposed therebetween at a third radial distance.   
     
     
       8. An electromagnetic clutch according to claim 7, wherein: an outer diameter of the contact member is substantially equal to that of the elastic member.   
     
     
       9. An electromagnetic clutch according to claim 7, wherein: the elastic member includes an arc shaped hole formed at a second radial distance thereof, the third radial distance being smaller than the second radial distance.   
     
     
       10. An electromagnetic clutch, comprising: a field member including an exciting coil member disposed therein;   a shaft extending through the field member and the exciting coil member;   a rotor member fixedly disposed on the shaft at a position therealong opposed to the field member;   a drive force transfer mechanism including a drive member rotatably received on the shaft, an elastic member mounted to the drive member and disposed on a side of the drive member facing the rotor member when the drive force transfer mechanism is received on the shaft, and a contact member fixedly carried on the elastic member in a position radially outward of a position of attachment of the elastic member to the drive member, the elastic member normally biasing the contact member towards the side of the drive member, the contact member being movable away from the drive member in an axial direction of the drive force transfer mechanism by deformation of the elastic member initiated by an applied force;   the drive force transfer mechanism further including a restricting member which presents a stop for restricting a displacement of the contact member away from the drive member to a restrictive distance in the axial direction prior to a reception of the drive force transfer mechanism on the shaft, the restrictive distance being less than a limit dimension representative of a maximum deformable amount of the elastic member beyond which the elastic member exceeds an elastic limit thereof and is permanently deformed, the elastic member being thereby protected against permanent deformation caused by an externally applied force thereto prior to mounted reception of the drive force transfer mechanism on the shaft; and   the contact member being positioned relative the rotor member to form a clearance of an operational distance in the axial direction between opposed surfaces of the contact member and the rotor member when the drive force transfer mechanism is mountably received on the shaft, the operational distance being smaller than the restrictive distance, whereby once the drive force transfer mechanism is received on the shaft, movement of the contact member in a direction towards, and subsequent engagement of the contact member with, the rotor member is unimpeded by the stop of the restrictive member, while protection of the elastic member against permanent deformation is maintained by the operational distance between the contact member and the rotor member.   
     
     
       11. A method of preventing damage to an elastic member during assembly of an electromagnetic clutch, the electromagnetic clutch including a field member, a shaft extending through the field member, a rotor member fixedly disposed on the shaft at a position therealong opposed to the field member, and a drive force transfer mechanism including a drive member rotatably received on the shaft, the drive force transfer mechanism further including the elastic member mounted to the drive member and disposed on a side of the drive member facing the rotor member when the drive force transfer mechanism is received on the shaft, and a contact member fixedly carried in a position radially outward of a position of attachment of the elastic member to the drive member, the elastic member normally biasing the contact member towards the side of the drive member, the contact member being movable away from the drive member in an axial direction of the drive force transfer mechanism by deformation of the elastic member initiated by an applied force, the method comprising the steps of: disposing a stop on the drive force transfer mechanism which limits movement of the contact member away from the drive member to a restrictive distance prior to mounted reception of the drive force transfer mechanism on the shaft, a resultant deformation of the elastic member when the contact member is moved the restrictive distance being less than an elastic limit beyond which the elastic member experiences permanent deformation, thereby protecting the elastic member from movement beyond the elastic limit thereof; and   mounting the drive force transfer mechanism on the shaft in a position in which opposed surfaces of the contact member and the rotor member are separated by an operational distance less that the restrictive distance, whereby movement of the contact member in a direction towards, and subsequent engagement of the contact member with, the rotor is unimpeded by the stop of the restrictive member, the stop, once the dive force transfer mechanism is mounted on the shaft, being separated from the contact member by the restrictive distance and being farther in the axial direction from the contact member than a contact member engaged surface of the rotor member.